Summary

All expressions of life ultimately depend on energy derived from redox chemistry and photosynthesis. On page 257 of this issue, Schuller et al. (1) report the structure of photosynthetic complex I at atomic resolution. The authors have analyzed how the distinct NADH [reduced form of oxidized nicotinamide adenine dinucleotide (NAD+)] dehydrogenase subunit S (NdhS) facilitates electron transfer from ferredoxin, thereby establishing efficient cyclic electron flow around photosystem I. The findings add an important piece to the puzzle of deciphering the enigmatic mechanisms at work in the remarkable molecular machines of the complex I superfamily encompassing photosynthetic and respiratory complex I, as well as proton pumping hydrogenases. In combination with high resolution structures of respiratory complex I from bacteria (2), mitochondria (3–5), and membrane bound hydrogenase (6), it is now possible to trace the modular evolution and functional adaptations of the complex I superfamily at the atomic level.